A hearing aid is a device used to help hard-of-hearing people
hear sounds better. In the past, a funnel-like amplification
cone, called an "ear trumpet" or "ear horn" was used. Also
sometimes used was a desk with a built-in amplifier into which a
microphone and earphones could be plugged; these worked better
than passive ear trumpets but were not portable.Now, however, the most common style is a small electronic device
that fits into the wearer's ear. The first variety of this
device had a rectangular battery pack connected by a thin wire,
intended to be held in a pocket. Such "body aids," though much
more portable than the desk type, still suffered significant
disadvantages due to sub-optimal microphone placement. Since the
microphone was not near the user's head, it was susceptible to
interfering sounds such as clothing-noise. Sound input was also
distorted if the microphone was located below the mouth of a
person with whom the user was conversing.